Thermally controlled electric relay



Nov. 29, 1949 E. c. THOMSON 2,489,391

THERMALLY CONTROLLED ELECTRIC RELAY (Hraey Nov. 29, 1949 E. c. THOMSON THERMALLY CONTROLLED ELECTRIC RELAY 3 Sheets-Sheet 2 Filed Dec. 9, 19.43

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E. c; THoMsoN THERMALLY CONTROLLED ELECTRIC RELAY 6a B/METALL/C No'a'. 29, 1949 Filed Dec. 9, 1943 0 9 Z Kl' \I Patented Nov. 29,1949

UNITED STATES PATENT OFFICE THEBMALLY y 2,489,391 coN'raoLLEn ELEcrmc amr Elihu Craig Thomson, Boston, Maas., assigner to Photoswitch, Incorporated, Cambridge, Maas., a corporation of Massachusetts Application December 9, 1943, Serial No. 513,563

(c1. zoo-122) s claims. l

This invention relates to electric switches and more particularly to thermally actuated rapidly -operating spring switches.

It is one of the main objects of the present invention to provide a switch o1 this type which on the one hand lends itself especially Well to rapid or snap operation and on the other hand to operation by a controlling condition which can be translated into a mechanical effect, for example by heat and, generally, to provide a switch of this type which is simple and rugged in construction and yet very sensitive, easily ady I switch of this type having tension and compression spring members whose switch elements are positively retained in operative relation with the temperature responsive controlling elements by the play of forces inherent in the construction as a whole, with a minimum of fastening elements; to providey a switch of this type who/se temperature-responsive elements are subjected principally only to tension; to provide a switch of this type which lends itself vwell to inexpensive, compact and yet safe assembly within a protective housing; and to provide electronic relay circuits which require very little output current, which are free from characteristics detrimental to the life of discharge tubes, and are generally advantageous under certain operating conditions.

In carrying out my invention I employ ilexible actuators firmly mounted at one point whereas another point of each actuator is positively connected with a corresponding point of the other actuator through a rigid link. At least one of these flexible members is thermoresponsive, formed vfor example of a bimetal strip provided with a heating resistance. A pointof the connecting link, between or on one side of the connected actuator points.' is associated with 'an operating member of the switch in question, for

realization of the above-mentioned objects since the two actuator members are rigidly coordinated, so as to combine their bending forces which forces depend upon the eiective temperature of the actuator; this temperature may be either ambient or determined by a controlling heater element.

In another aspect of the invention, the actuators are strips arranged in the general direction of the lines of stress of the spring members of a snap switch. The connecting link is fastened to one spring member so as to operate it. If the connector or link is thus joined to actuvators and switch spring, forexample with the actuatorstensioned to take up the stress of the tension member of the switch. the operative associationof actuators, connector and switch member is positively sustained in the simplest possible way. This mode of correlation also has the advantage of subjecting the actuators almost entirely to axial stress, thus largely avoiding unfavorable bending moments which might affect the accuracy of operation.

'Ihese and other objects, aspects and features will be more -fully apparent from the following description of several practical embodiments illustrating the genus of the invention. The description refers to drawings in which Fig. 1 is a side view, with a.front cover block removed, of a switch according to the present invention with two individually heated actuators;

Fig. 2 a section on line 2-2 of Fig. 1;

Fig. 3 a section on line 3--3 of Fig. l;

Fig. 4 an expanded section of the switch elements proper, on line 3 -3 of Fig. 1;

Fig. 5 a side view similar to Fig. 1 but with both cover blocks removed;

Fig. 6 a front view of a second embodiment of the invention with one heated actuator;

Fig. 7 a section on line 1--1 of Fig. 6;

Fig. 8 the verticalsection, similar to Fig. 2, of

va third embodiment of the invention in which the actuators are noty provided with heating elements;

Fig. 9 an axonometric view of the insulation sleeve upon which the heater is wound as shown Fig. 10 an axonometric representation of the switch spring, in two embodiments;

Fig. 11 a schematic representation of an embodiment of the invention with the' actuators on one side of the switch; and Fig. 12 the diagram of a circuit incorporating a switch according to the invention.

In the embodiment shown in Figs. 1 to 6, the

switch according to the invention is mounted in an insulating housing made for example of molded plastic. The housing herein shown and described is of a construction which is particularly suited for this purpose but which is not part o! the present invention and constitutes the subject matter of copending application Serial No. 513,571 filed on December 9. 1943, now Patent 2,418,831, April l5. 1947. This housing consists of a mounting block I and two similar cover blocks 2 and 3. the three blocks being held together by screws 3. 1, l. Screws t and 1 tit into threaded inserts or nuts |6, |1 (Fig. 3) molded into block with their ends protruding into a recess 23 having an upper straight portion 2| and having a rounded bottom portion, as shown in Fig. 5. Holes |2, |3 may be provided in blocks I, 2, 3 for the purpose o1' suitably fastening the switch to a support. Ventilating slots Il. I may be provided as indicated in Fig. 3.

Two heat-responsive actuator strips 22, 23, for example of bimetalic construction, have on one side widened ends with holes 25 (Figs. 4 and 5) which are slipped over the protruding ends oi inserts I6, |1,as shown in Fig. 3, recesses 20 preventing strips 22, 23 from rotating on the nuts. The strips are held in place by bosses 26, 21 of cover block 2, 3 (Fig. 3) which ilt into recesses 23 of block I.

The actuator strips may be provided with coils 32, 33 constituting heating resistances, preferably wound on insulating sleeves 3| of the type shown in Fig. 9. The ends of the heater wire or wires may be connected to terminal bars 36, 31, 33, 33 which have V-shaped deformations 4| and ilt into corresponding recesses 42 of block I wherein they are positively confined by the cover blocks 2 or 3 when the blocks are screwed together. I! one or both actuators are not to be artificially heated, some or all of these bars may be omittted, as for example indicated in Fig. '1 where actuator |23 is bare. In that case, mounting block-i does not have recesses 42.

Molded into mounting block are further two pivot bars 5|, 52 whose protruding ends are provided with pivot notches 53. 54 (Figs. 1, 2)

A connecting means such as bar or rod 55 joins the free ends of actuators 22 and 23, the ends of bar 55 being secured within holes 24, for example by means of peripheral recesses 51 which arrangement provides pivots permitting free movement oi the actuators while strictly maintaining their distance.

A switch spring 60 (Fig. 10) has two compression members or branches 6|, 62 and therebetween a tension branch 63. The common portion 64 carries a contact point 65. The end of the tension branch 63 is shaped to engage an intermediate point, preferably a groove 63, of connecting bar 55, for example by means of a perforation 66 or a hook 60 (Fig. 10). The ends 13,14 of the compression branches 6|, 62 rest in the pivot notches 53, 54 of supports 5|, 52. Tension branch I3 is shorte than compression branches 6|, 62, so that the latter will buckle slightly when opening 66 engages connector 55 and the compression branches rest in notches 53, 54, provided of course that, as shown in the present instance, the notches are arranged approximately at the height of the connector.

In the figures, the contact 65 is shown in central position between faces 02 and 03; it will be understood that this position has been selected 4 for the sake of convenient representation only to Fig. 8 may be used to advantage.

' 4 and that the movable contact will always rest on one or the other of these faces.

The contact point l5 cooperates with contact faces 32, 03 which are part of contact bars 3l, 35 molded into cover blocks 2 and 3 which have rocesses 36. 61 forming together a chamber connning the contact point 65. The contact bars 34, Il are preferably L-shaped and bent outwardly. and protrude from blocks 2 and 3 with terminal ends 60 and 60 which, in order to provide proper spacing, may thus be staggered as indicated in Fil. 1. 'I'he terminal for the double throw switch spring 60, making contact either at 32 or 33, may be at 90, the' circuit leading from contact point Il through branch 63, bar 55, actuator 22. or 23. nut I6 or |1 to screws 6 or 1, either of which may be used as a terminal. It it is desired to use only a single stationary contact, as for example in the circuit of Fig. 12, one of the contact bars Il, 3l may be omitted, as shown in Figs. 6 and '1.

The above-described embodiment is especially well adapted for differential actuation when both actuators are provided with heaters as shown in Figs. 1 to 5, or for use with only one heater on a controlling actuator while the other actuator oompensates for ambient temperature within the switch.

If it is desired to apply to one actuator the temperature of the general environment rather than that of the switch structure, an embodimfn f may be preferable which is similar to that shown in Figs. 6 and "I which will now be described.

In the embodiment according to Figs. 6 and '1, a mounting block |0| carries threaded inserts or nuts H6, ||1 holding actuators |22, |23 and con- Vnecting to terminal in a manner similar to that described with reference to Figs. 1 to 5. The single heater coil |32 is connected to a pair of heater terminals |36, |31. The mounting block |0| `is extended upwardly beyond spring |33 and forms one half |31 of the chamber which encloses contact point |65 and provides an insulated stop for this movable contact.

The contact face |82 of an L-shaped bar |04 is moulded into a cover block |02 which is fastened to block by means of screws |06 and Ill. Pivot supports |5|, |52 with notches |53, |54 are again moulded into block |0|, and the arrangement of actuators |22, |23, screws |05. |01, connecting bar |55, and switch spring |60 with branches IBI, |62, |63 is similar to that described with reference to Figs. 1 to 5.

The connector |55 reaches actuator |23 through an opening |20 which, if desirable, may be lined fwith heat-insulating material. It will be understood that opening |20 can be made sumciently wide to insure equal ambient temperature for both actuators; such a construction may for example be used in the circuit to be described with reference to Fig. 12.

The bare actuator |23 may be protected by a slotted cover plate |04 having a boss |21 tting into the corresponding recess |42 of block |0| and holding actuator |23 by means of screw |01; a top flange ||0 ts a corresponding groove of block |0|. Holes |I|, ||2 may be provided for fastening the switch to a support.

Ii it is desired to apply the temperatures prevailing at two separate points by means of two bare actuator strips an to render the operation of the switch dependent upon the relation of these temperatures, an arrangement according In this figure, the mounting block 20| is provided with a flange 205 by means of which it can be fastened to a wall 200 separating the spaces at different temperatures.

The block 28|, similar to block I shown in Figs. 1 to 5, has moulded-in nuts 2li and 2I1 holding the actuator strips 222 and 223 and the notched pivot bars of which only bar 251 is shown. Connecting bar 255, together with the pivot bars, holds the switch spring 238 in the above-described manner. Nut 2H may be contained in a boss 2I8 of block 28| which protrudes through an opening in wall 23| and carries, fastened thereto by screw 281. a slotted cover plate 203. A second slotted cover plate 282. fastened to block 20| by screws 288 and 258, carries contact bar 288 moulded thereinto, opposite a contact bar 283 similarly fastened to block 20|. The contact point 285 is arranged between contact faces 282 and 283 of bars 288 and 238, as above described. In order better to separate the medium surrounding actuator 223 from that surrounding actuator 222, a heat insulating bushing 250 may be provided for leading bar 255 through wall 200.

It will be understood that the current-carrying connection to the movable contact 55 must not necessarily lead through one of the actuator strips, but that it may be preferable to connect this contact directly with a conveniently placed terminal, for example through a flexible cord.

It will further be understood that the tension branch 63 of the switch spring must not necessarily be attached to the connector between the actuators 22 and 23, but that it may be arranged on the outside, as shown in Fig. 11. In this iigure, 355 is the connector which correlates actuators 322 and 323 with switch spring 350. 332, 333 are the heater coils, 351 a notch of connector 355 for pivoting actuator 323, and 359 isa similar notch for the tension spring. Contact point 355 moves rapidly/between fixed points 382. 383 when connector bar 355 is slightly moved in one or the other direction, by the combined effect of the actuators. It will be evident that, by appropriate choice of the lever arms, the tension forces and stresses involved can be selected at will, to suit any particular purpose. Similarly, the connector 5-5 may be of any convenient construction suiciently strong to support the loads applied A thereto.

The above-described devices operate as follows.' The pivot points 54, 51,53 (Fig. 4) of the actuator and switch spring system are so adjusted actuator is towards the lea or mg. a outweighs that of actuator 22 towards the right. Bar 55 will then move towards the left, thereby causing the lines of stress of the switch spring branches to pass each other and point B5 to move rapidly towards the right, connecting terminal 83 with terminal 88 instead of 88. At the same time, any ambient temperature eifect'is inherently excluded so long as the actuators are not deliberately kept separated as for example in the embodiment according to Fig. 8. It will be evident that, in arrangements similar to that of Figs. 1 to 5, any change in ambient temperature will affect both actuators equally but in opposite direction, the two virtual deflections cancelling each other. Upon reversal of the temperature relation of the two actuators, the switch will move back into initial position. It will be understood that the actuators must not necessarily deflect in opposite directions, although this is necessary for ambient temperature correction. Generally speaking, the switching operation will depend on a differential, additive or subtractive, effect of ambient and controllably impressed temperatures.

If only one heater element is used, as in the` embodiment according to Figs. 6 and 7, the second actuator merely provides compensation for ambient temperature changes, rendering the effect of the actuating heater I 32 lindependent of the ambient temperature so that it can be safely relied upon to operate the switch when its heating current attains a definitely determinable value.

In embodiments where the two actuators are -not aifected by the same ambient temperature conditions', as for example in that shown in Fig. 8,

. switches according to the invention can be operthat contact point assumes under normal deflect inwardly with rising temperature, if their rate of deilection is the same and their heater elements similar, the switch will remain in normal position so long as the currents in the respective coils are the same, in which case the equal tendencies to deflect in opposite directions cancel each o er. If, however, one heating effect and hence the corresponding deection outweighs the other, the switch will be operated. Assuming for example that point 55 rests normally on contact face 82 and that the actuators deflect inwardly with rising temperature, the contact point will rapidly move from face 82 to face 83 when heater 33 becomes so much ated responsive to an absolute diiTerence of` two temperature conditions. These temperatures may be either ambientones or, if one or both actuators are provided with heating coils, a combination of ambient and superimposed control temperatureswill be eiiective in operating they switch, as distinguished from the operation of switches according to Figs. 1 to 5, where a com` bination of two controllably impressed, temperatures is effective, and of switches according to Figs. 6 and where the absolute value of a controllably impressed temperature is effective.

Switches of the above-described type can beused in any circuit permittingthe inclusion of heating elements and -not requiring absolutely instantaneous operation, or where instantaneous operation is even undesirable but where two temperature conditions, one of which may be an ambient temperature, have to be exactly and positively correlated.V y

By way of example, a circuit will now be described whose accurate operation is made possible through temperature correlation according to the present invention, and in which the time lag inherent in this compensation is a beneficial factor.

Referring to Fig. 12, A and B are the terminals of an alternating current supply source, to which are connected a potential apportioning network VN with impedances RI and R2, and an electronic discharge device, for example a gas-lled cold cathode tube T with anode a, cathode ,Ic and con- `trol electrode c. Impedance Riv maybe bridged by a variable-impedance detecting device, for example two electrodes or probes pl, p2 associated with a tank t for a liquid l. The control electrode RI and R2.

warmer than heater 32 that the deflection of 75 The heater coil 32 of bimetal strip 22 of a switch is nonconductive.

B according to the present invention is connected in the anode circuit oi tube T. The switch may be mounted in a housing according to Figs. i to a single throw switch being used in this embodiment. An insulating stop as shown for example in Fig. 7 is indicated at IM. The contact indicated at I! may be connected to terminal A through a signaling device D, and the terminal M of the switch spring il may be connected to terminal B. The potential apportioning network may be so arranged that, when the probes pl, p2 are above the liquid level and constitute a high impedance, the potential of c is such that tube T The switch S may be so arranged that, with the tube nonconductlve, bar il is in a position retaining contacts 65, I2 open with blade 6l resting against stop lll.

In an arrangement of this type reliable compensation for ambient temperature is an important factor since, because oi' the comparatively low current and the correspondingly slight temperature changes available in the load circuit oi auch ay device, variations in ambient temperature might be suiilcient to cause false operation o! an uncompensated switch. t

In the circuit shown, control electrode c will normally have a potential effectively blocking current now through the tube. Heater v32 then does not carry appreciable current and contact 6l rests against the insulating stop lOl. I! the water l in tank t rises until probes pl, p2 are conductively connected, the potential drop across .impedance Rl will be decreased, the potential of c will rise and the tube become conductive. The output current ilowing through coil l2 heats actuator 22 which moves bar 55 towards the right and causes point 65 to snap into contact with sta- .tionary contact B2. energizing' signaling device D.

Since both actuators tend to deflect towards the middle, and both are exposed to the same ambient temperature, no net motion results from variations in ambient temperature and the switch responds solely to changes of the tube output current.

The slight time lag between the tiring of the tube and the closing of the switch upon coil 32 reaching the required temperature, which time lag can be easily adjusted to any suitable value, eliminates false operation in response to momentary etlects, such as splashing of water over the probes. Another beneficial operating feature inherent in a circuit or this type is due to the purely ohmic character of the load resistance in the output circuit of the discharge tube. A load of this type utilizes all available energy, even of alternating current components oi irregular wave shape. The current passing through a vacuum or gas tube to which an alternating voltage is applied, has the coniiguration of a rectified wave. The heating of the tube is proportionate to the etlective or R. M. S. value oi the current wave. but the useful power available to a conventional magnetic relay in the plate circuit of the tube is proportionate to the average current which is less than the R. M. S. value. Ii the unused alternating current component is by-passed around the relay by a' condenser, this component contributes to the heating of the tube increasing the detrimental peak tube current, while it does not contribute in any way to the useful power of the relay.

It, according to the invention, a thermal relay is used, the power, available therein is propor- -tionate to the eilective or R. M. S. value of the tube current which is greater than the average current; elimination of the alternating current Lbypass or smoothing condenser reduces the peak tube current. The conventional connection of a condenser in parallel with a magnet coil in the output circuit of a tube. passes high surge currents. which are detrimental to the life of the tube. These surge currents can be limited by series resistances but only at some sacrice in eiciency. It a pure resistance, as represented by the heater coil of the present relay, is used in the anode circuit, the peak current is limited to a value much lower than that obtainable in any circuit containing a capacitance.

From the foregoing description it will be apparent that the present invention is not dependent upon any particular construction of the snap switch proper but that the interconnected thermally controlled actuators may ailect the operation initiating element of any switch that is at all suitable for this purpose. Ii the invention is applied to switches of the type herein described, it is not necessarily limited to constructions where connector 55 is attached to the tension member of the switch spring but, obviously, this connector can be fastened to the compression springs, so long as movement of the connector provides ior relative movement of the spring branches causing passing of their lines oi stress.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims I claim:

1. A thermally controlled snap switch comprising: a support; a first thermal actuator, mounted on said support, having a free portion which moves in response to a temperature change; a second thermal actuator adapted to prevent motion oi said iree portion in response to an ambient temperature change equally eilective on both actuators; two spring members joined together at one end', one spring member being so mounted on said support, and the other so secured to said tree portion as to be subjected to opposite conditions of stress, and thereby arranged to cause abrupt movement of said joined ends when said tree portion passes through a predetermined position relative to said support; an electrical contact arranged to be operated by said abrupt movement; and heating means arranged to cause dii!- ferential heating of said actuators, and thus give rise to said abrupt movement.

. 2. A switch according to claim 1 in which said actuators comprise two bimetal strips, each strip having an end fixed to said support and a free end, and said free ends being connected by a rigid member.

3. A thermally controlled snap switch comprising: an actuating unit including two cooperating thermal actuators of such characteristics as to bend equally in response to a given temperature change, each actuator member having a mounting portion and a movable actuating portion; means for rigidly connecting said actuating portions; means for supporting said mounting portions so that the bending tendencies of said actuators oppose each other thereby preventing motion of said connecting means in response to a temperature change equally effective on both actuators; two spring members joined together at one end, one spring member being mounted on said supporting means, and the other so secured to said connecting means as to be subjected to opposite conditions of stress and thereby arranged to cause cause abrupt movement of said joined ends when said connecting means passes through a predetermined position relative to said supporting means; an electrical contact arranged .to be operated by said movement; and heating means associated inheat transfer -relationship with one of said actuators.

4. A switch according to claim 3 wherein said connecting means comprises a rod, and the spring member secured thereto is pivoted with respect to the rod.

venting motion of said free ends in response to a i temperature change equally effective on both f. strips; a snap switch unit including a tension member, means for pivoting the unattached end of said tension member on said rod, and means 5. A switch'according to claim 3 having two independent heating means, one associated in heat transfer relationship with .each of said actuators, the position of said connecting means being determined by the differential in heating effect of said independent heating means.

6. A thermally controlled snap switch comprising: an actuating unit including two cooperating thermal actuators of such characteristics as to bend equally in response to a given temperature change. each actuator member having a mounting portion and a movable actuating portion; means for rigidly connecting said actuating portions; means for supporting said mounting portions so 'that the bending tendencies oi said actuators oppose each other, therebypreventing motion of said connecting means in response toa temperature change .equally eiective on both actuators; a snap switch unit including a tension member, a compression member adjacent thereto and attached at one end to an end of said tension member, means for pivotingthe unattached end of said tension member on said connecting means, and means for pivoting the unattached end of said compression member on said supporting means, said pivoting means being arranged to put said members under compression and tension, respectively, and thus cause rapid motion oi' said attached ends upon passing of the lines of stress of said members when said respective pivoting means are moved relative to each other; lan electrical contact arranged to be operated by said rapid motion; heating means associated in heat transfer relationship with one of said actuators; .and stops mounted on either side of said attached ends in xed relation to said supporting means.

'7. `A thermally controlled snap switch comprising: asupport; two bimetal strips having such heat-responsive characteristics, andeach having an end so ilxed on said support, as to bend equally in opposite directions in response to a change in ambient temperature; a rod rigidly connectingv the free ends of said strips sol as to combine their bending tendencies., thereby prefor pivoting the unattached end of said compression member on said supporting means, said pivoting means being arranged to put said members under compression and tension, respectively, and thus cause rapid motion of said attached ends upon passing of the lines or stress of said members when said respective pivoting means are moved relative to each other; an electrical contact arrangedto be operated by said rapid motion; heating means associated in heat transfer relationship with one of said actuators; and stops mounted on either side of said attached ends in fixed relation to said supporting means, and a heating coil wound around one of said strips. I

8. A switch according to claim 7 having a sec- `-cndheating coil wound around the other of said 25y REFERENCES CITED The following references are of record in the Number Name Date 1,734,095 Mancib Nov. 5, 1929 1,920,646 Kroger Aug. 1, 1933 1,960,068 Ruppel May 22, 1934 2,027,405 Smede Jan. 14, 1936 2,049,355 Cockrell July 28, 1936 2,144,120 Parks Jan. 17, 1939 2,189,996 Riche Feb. 13, 1940 2,202,197 Ewertz May 28, 1940 2,223,460 Riche 1.--, Dec. 3, 1940 2,265,203 Six Dec. 9, 1941 2,272,021 Riche Feb. 3, 1942 2,297,841 MacKenzie Oct. 6, 1942 2,388,812 Albin Nov. 13, 1945 2,399,901 Wald May 7, 1946 2,418,831 Hamilton Apr. 15, 1947 2,441,979

schmmmger et e1. my as, 194s 

